As for occupying captured cities. You take a city, your maintainace costs go up while its spends turns in resistance unable to produce anything. Small cities its not that bad but larger cities can take over 15 turns or more sometimes. It goes out of revolt your mainatianace costs go up even more but the city still needs to be built up from scratch and may even be going into starvation since it hasnt gotten its full border pop yet and/or still swamped by culture from other cities that havent been taken yet. With very rare exceptions like a shrined holy city or city with important wonders that havent obselted yet most captured cities are a drain on your empire for MANY turns before they are actually productive.
Meanwhile you STILL have to occupy or risk losing it. You have to deal with "we yearn to join our motherland" unhappiness in that city until/if you completely destroy that civ. Not ot mention the fact that that city is very vulnerable to going back into culture revolt from the culture of the enemy cities around it (or worse actually flipping over to a third civ). And thats assuming AP/UN liberate votes wont be an issue.
All of which brings up the questions as to exactly why all this needs to be even more of a pain to deal with?
Kaytie